Twenty years after DNA was first used to exonerate a man, capital-punishment opponents are optimistic.

The number of people receiving death sentences is declining, Rust-Tierney said. Legislation to reform or repeal the death penalty is now regularly introduced in states across the country. And perhaps most significantly, longtime death-penalty opponents have been joined in the trenches by civil rights activists and those with the political experience and social standing to raise real questions about inequality in the criminal-justice system.

In fact, since 2000, death-penalty sentences handed down by state courts and juries have declined nearly 75 percent, and the number of executions has been cut in half, said Richard Dieter, executive director of the Death Penalty Information Center, a Washington, D.C.-based anti-death-penalty nonprofit.

One explanation for the change: Crime itself has declined, said Dieter. Another is that the nation’s increasingly cash-strapped states have looked at the cost of the death penalty and the multiple appeals and hearings that almost always follow, he said. Longtime death-penalty opponents wish, Dieter said, that arguments about the uneven nature of death-penalty sentences had made the difference.

“It’s a combination of a lot of things,” Dieter said. “But if I had to point to one thing, it’s innocence, the possibility of actual innocence. DNA testing has revealed to the public that in so many cases where people thought the right person was on death row, [it] turned out to be wrong. DNA has produced some growing awareness of the irrevocable and fallible nature of the death penalty.”

It’s the so-called CSI effect. Juries want proof. And even in states such as Texas — the longtime national leader in executions — beginning this year, prosecutors will be required to make sure that any evidence that can be tested for DNA material undergoes that process before a jury is asked to impose the death penalty. And all of the 32 states that maintain the death penalty also now give juries the option of sentencing defendants to life without the possibility of parole.

In 2012 and 2013, legislatures in Connecticut, Maryland, Delaware and Colorado considered repealing the death penalty. Only the Connecticut and Maryland measures became law. But Colorado’s governor did institute a moratorium on executions.

Longtime death-penalty opponents say that the increasing involvement of new voices in the movement to abolish capital punishment has also played a significant role in the slow state-by-state death of capital punishment. One of those new voices: the NAACP.